monday night after a holiday weekend rocked by so many questions about that plane crash in san francisco. You are looking live at the remains of asiana flight 214 still sitting beside the runway, a charred clue to a mystery. Tonight passengers and seasoned pilots across the nation asking how could this happen on a commercial flight with professionals at the controls and what about the 7 seconds when life and death decisions were made in the cockpit. David muir leads us off he is there tonight and we begin with you. Reporter: Here's another view of the fuselage still sitting beside the runway. So many passengers coming in on run ways just jis sent to that aircraft. Tonight as you mentioned the final seven seconds, the chaos in the cockpit revealed. New images of the determined passengers fleeing to get out alive. You can see the emergency shoots inflate. Passengers sliding down them, racing to get away from the plane. The family capturing he is images stunned at what they were seeing. That's scary. Reporter: With a cloud of dark smoke growing some of the passengers can be seen running for their lives at the end of the runway. All of this unfolding after the crucial 7 seconds that decided the fate of this flight. The pilot in charge, in training. From one of the black boxed we learned that 7 seconds before impact a call from the cockpit, the pilot suddenly looking to increase speed, the jet hovering far too low over the water. Then just four seconds before impact the jet approaching the sea wall and from the black box the sound of what's called the stick shaker,en urgent warning mechanism that literally shakes the pilot's hands as seen here. That shaking telling the pilots the jet was suddenly moving too slowly to pull off a safe landing. Then just a second and a half before impact a call from the dock pill for go around to circle the airport again. It was too late. The taheering off the back of the plane. At any time the ntsb investigate the crucial 7 seconds and the pilot in training. The airline says he was experienced in other aircraft but 43 hours training time on this plane. Is that enough for this airport? There's always going to be the first time for someone to land at a different airport. The co-pilot just as important there to guide him. A clear view of the different shades of horror the passengers faced depending on where they were sitting. This passenger surveying the wreckage from the plane. He was sitting in 30 k. The very seat next to the door, yes. Reporter: The challenge for him, that exit shoot mangled. He had to help passengers climb down out of that door using the debris as stairs. This woman, seat 40 c traveling with her 4-year-old son who broke his leg. You could see the flames through the windows. This man in 3 k dumped up to business class before the flight. Those rows intact. A stroke of luck because the front of the plane was the first to catch fire. The second door is where you climbed out. Reporter: Tonight the firefighters first to respond climbing into the burns plane where they found trapped passengers in the back. You could see smoke coming right out the door there. Could you see the fear in their faces? I think it was more shock that I saw. I didn't see fear. I saw shock. Reporter: This evening new images of the two girls lost, the 16-year-old school girls from china. The fire chief telling me the investigation under way into the very real possibility that one of them might have been hit by one of the rescue trucks during the chaos. As a community back home remembers the young girls who formed that heart over their head with their arms. That would be just another heartbreaking development. I wanted to share with you me, the ones who entered the plane while he it was burning. You can see the orange end of the plane, that's the tail that ripped off. They formed a sort of human chain to the back of the plane carrying the final passengers who were trapped down to safety. So many stories of heroism emerging here. Thank you david and thank you for all the great reporting this weekend. As you said, there are so many stories that have everyone defining courage tonight. One of them we are talking about flight attendants on the plane. And a tiny fearless young woman who with quick thinking and super human strength saved a lot of lives. Reporter: She was the very last person to make it out alive. Then trying to make one final run to the back of the burning plane to be sure she left no one behind. Translator: I had to hurry. I couldn't think of the danger to myself. Reporter: That's the lead flight attendant with a child clinging to her back running as far away as she could. Other survivors say she carried people twice her size to safety. She was so tiny and skinny. I couldn't believe how powerful, how strong she was. She was helping other flight attendants and even outside of the plane, after she got off the plane just running around the plane without fear. She was really brave. Reporter: So brave she stayed to make sure everyone was okay, watching over as paramedics treat the passengers she had just saved. She was so composed I thought she had come from the terminal. She mentioned she was on the plane. She was a hero in my mind. She is the sully sullenberger of flight 214. Translator: The child was afraid to go down the slide so i tried to encourage the child, put him on my back and slid down. Reporter: Through it all she says the only thing on her mind was rescuing the next passenger. What she didn't know is she rescued all of those passengers one by one and she, too, was hurt. She broke her tailbone she thinks during the crash landing. She only found out when she went to the hospital later that day and was told pie doctors. Diane, a true hero. Thanks to cecilia vega. I want to bring in a pilot investigate. You wanted to show us what it looks like if you had a perfect landing. This would be an average day. The pilot is stabilized on the glide path. The airplane is on speed. In this case what happened with these pilots on this plane is they are coming in at about 82 seconds out. You say they don't know anything is wrong? No. Everything is good until 82 seconds. Then the pilot disconnects all the computers and takes over manly. He should not have disconnected everything. No because the engines are back at idle. He's flying manuelly and at the very end the airplane is so slow it's below the speed. When we look at the experience of this pilot in this plane, 43 hours, is that a central explanation? What do we know? The co-pilot was the one who was really in charge of this flight. He was the check airman, the strucker, he was the guy who was supposed to be teaching how to fly the airplane. He failed to notice nobody was working the engines. Having an experienced pilot in the co-pilot seat should have been fine. This happens all the time? Happens all the time. Thank you, corn medical.

This transcript has been automatically generated and may not be 100% accurate.

Lessons in plane safety, and what passengers need to do to stay safe onboard a plane.

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